Filament



t 25 ciently to result- Paten ted Dec. 18, 1928.

UNITED STATES- PATENT OFFICE.

IEREDEIRJIGIK HOLBORN, OF HAGKENSACK, JERSEY, ASSIGNOR TO BE FOREST RADIO TELEPHONE & TELEGRAPH (10., OF JERSEY CITY, NEW JERSEY, A CORI'ORA:

TION OF DELAWARE.

Noprawing.

This invention relates to filaments and more particularly to filaments which are used in electron discharge devices.

' The objects of the invention are to provide a filament havinga high electron emissiveness; to provide a'filament which is madeup of materials not too expensive for practical purposes; to utilize materials in the'filament which have melting points close enough to-- gether to enable the ingredients tobe worked together; to utilize an alloy which is made with comparative ease. and which may 'be drawn into suitably fine wire to use as a filament; to secure simplicity and durability of construction,

and results as may be brought out in the following description.

In the manufacture of filaments for use in electron dischar e devices, it is necessary to employ some substance which is sufficiently emissive as to render the completed device effective. It is also necessary to employ some substance through which a current may be passed and which will become heated suifiin ionization. One of the principal elements which has heretofore been used is tungsten, and as a later developmentthe element thorium has been extensivelyused.

In the present invention, I prefer to use nei ther of these elements, but have discovered that it is possible to use an alloy, or solid solution, of a base metal with an emissive metal. There area number of such combinations which may be used and for the purpose of this application I make particular mention of iron as constituting the base metal and lith-v mm as representing the emissive substance. These elements may be combined by any suitable process and drawn so as to provide a wire usable as a filament. It is' to be understood that there may be various wa s of combining these two metals, either y mixing or coating so long as the lithium is in substantially pure and active state for obtaining the electron emission. The preferred .Way in which I combine the two metals is by first amalgamating the lithium, that is, mixing i and kneadin same with mercury. With the lithium ama gam I mix a qu-antity ofiron.

in powdered or finely divided stateobtaining thereby a homogeneous mechanical mixture, which I then heat. 7 The melting point of the mixture is less than the melting point of and to obtain other advantages FILAMENT.

Application filed January 9, 1924. Serial No. 685,182.

iron, but is sufficiently greater than the vaporization point of mercury so as to vaporize the mercury and leave the mechanically mixed iron and lithium which thereafter melt.

I then allow the molten mass to cool so as to form the alloy or solid solution. This alloy probably consists of a mass of iron in. which lithium is carried in suspension. However, I have not had the opportunity to thoroughly investigate the alloy to determine whether it is strictly a mechanical mixture or solid solution, or whether there is a chemical combination. I suppose that it is most likely a solid solution as suggested above..

After the alloy or solid solution'has been made as above described, the same can be drawn very readily into wire form of as small diameter as desired, and will have a very uniform diameter and will be highly emissive. It will be noted that the particular ingredientswhich I have mentioned above as representative of the base metal and emissive substance, are relatively cheap so as to enable the filaments to be made with reasonable exsubstances, and have made mention of iron and lithium heretofore for the purpose of being definite only. However, there are other materials I have in mind under'the general heading, and of these I believe nickel to be a very good substitute or equivalent of iron as the base metal or material." In fact, results obtained with the combination of lithium and nickel almost equal results obtained with iron and lithium.

Obviously other changes and modifications may be madein the manufactureof my improved filament, and I do not wish to be understood as limiting myself to the details of the fore" oing description except as set forth in the fo lowing claim when construed in the light of the prior art. Having thus described my invention, I claim:

A cathode comprising a combination of iron and lithium.

FREDERICK Horizon 

